1. Field of the Invention
The present invention relates to a method for transmitting and receiving inter-radio access technology (inter-RAT) information between a mobile station and a base station for inter-RAT handover in a radio access system. The present invention also relates to a new header structure and a data transmitting and receiving method, for supporting inter-RAT handover.
2. Discussion of the Related Art
Exemplary embodiments of the present invention describe handover between different networks, i.e., inter-RAT handover. Hereinafter, general handover and inter-RAT media independent handover (MIH) will be described in brief.
Handover refers to a function that allows a mobile station (MS), which is making a call, to continue to maintain the call even when the MS moves from a service area of a base station (BS) to a service area of another BS in a communication zone such as a mobile communication cell.
Handover occurs when a radio channel within a BS to which an MS belongs is in a poor state, when an MS moves from a current sector within a BS to another sector, and when an MS moves from a current BS area to another BS area.
Handover may be divided into softer handover, soft handover, hard handover, etc. according to how a radio channel is switched.
Softer handover is carried out within one cell and refers to switching to a good channel from among channels used by an MS within a cell coverage. Soft handover refers to a process in which an MS simultaneously uses two neighboring channels and gradually disconnects one of them in the end. A code division multiple access (CDMA) scheme can easily achieve soft handover because MSs use the same frequency band. Hard handover refers to a process in which an MS stops using a current call-connected channel and immediately connects to another channel.
Handover may be divided into a network controlled handoff (NCHO), a mobile assisted handoff (MAHO), and a mobile controlled handoff (MCHO), according to who performs handover.
Intra radio access technology (intra-RAT) handover supports handover between homogeneous networks. Intra-RAT handover provides seamless handover and service continuity when an MS moves from an area of a BS (e.g., a serving BS) controlling the MS within a homogeneous network to an area managed by another BS (a target BS), thereby increasing MS user convenience.
Inter-RAT handover (or, Inter-RAT network handover) supports handover between heterogeneous networks using different radio access technologies. For example, inter-RAT handover is carried out when an MS moves from a cell area of a serving BS within a homogeneous network to a cell area of a target BS within a heterogeneous network. The inter-RAT handover may also be called handover between heterogeneous networks or MIH between heterogeneous networks.
Institute of electrical and electronic engineers (IEEE) 802.21, which is currently under development for an international standard concerning MIH between heterogeneous networks, is designed to increase MS user convenience by providing seamless handover and service continuity between heterogeneous networks.
The IEEE 802.21 standard supports handover between different radio access networks to improve user experience and support cooperative use of information used in an MS and a network. To this end, an access point of a network, such as an MS and a BS, should provide a multi-mode. This means that plural radio standards can be supported and, simultaneously, connection on a radio interface can be permitted.
An MS may be a multi-mode node supporting one or more interface types that take various forms. For example, the interface types may be a wire-line form such as IEEE 802.3 based Ethernet, a radio interface form based on an IEEE 802.XX-series wireless interface including IEEE 802.11, IEEE 802.15, or IEEE 802.14, and an interface defined by a cellular standard institute such as 3GPP or 3GPP2.
A multi-mode MS includes a physical layer and a media access control (MAC) layer of each mode. An MIH layer is located under an Internet protocol (IP) layer. An MIH function (MIHF) of an MS is a logical entity and may be freely located within a protocol stack while interfacing with each layer through a service access point (SAP).
MIH is preferably defined between IEEE 802-series interfaces or between the IEEE 802-series interfaces and the above-described non-IEEE 802-series interfaces (e.g., 3GPP or 3GPP2). To provide seamless service when a user performs handover, it is desirable that the MIH support a mobility support protocol of an upper layer such as mobile IP and session initiation protocol (SIP).
MIHF, which is a logical MIH entity, allows an MS to perform inter-RAT handover. An MS and a network may include MIHFs. The MIHFs serve to transmit and receive information about setting or state of an access network around the MS.
The MIH entity is located under an upper layer including an IP layer and defines handover between an IEEE 802-series interface and an interface defined by 3GPP/3GPP2, as well as handover between IEEE 802-series interfaces. Namely, the MIH entity obtains information about heterogeneous networks from a second layer to facilitate inter-RAT handover. Meanwhile, the MIHF may exchange MIH signaling using information from a third layer, such as user policy or configuration.